.box {
  width: 400px;
  height: 200px;
  line-height: 200px;
  text-align: center;
  color: #fff;
  background-color: #000;
  font-size: 30px;
  position: absolute;
  left: 50%;
  top: 50%;
  margin-left: -200px;
  margin-top: -100px;
}